Tolerance compensation in a reusable clamp structure
||Tolerance compensation in a reusable clamp structure
||August 10, 1999
||February 4, 1997
||Oetiker; Hans (Horgen, CH)
||Hans Oetiker AG (Horgen, CH)|
||Bryant; David P.
|Attorney Or Agent:
||Birch, Stewart, Kolasch & Birch, LLP
||24/20R; 29/407.01; 29/DIG.37
|Field Of Search:
||29/407.01; 29/407.05; 29/407.08; 29/DIG.37; 72/333
|U.S Patent Documents:
||4773129; 4998326; 5283931; 5402554; 5669113
|Foreign Patent Documents:
||A clamp structure with a clamping band which can be used, for example, to fixedly secure a hose on a nipple and which includes a tightening arrangement for tightening the clamp structure about the object to be fastened and a tolerance-compensating arrangement for the entire tolerance range of the hose and nipple. The tolerance-compensating arrangement is thereby formed by a slot-like opening punched-out of the clamping band which is of such width and length that the lateral clamping band portions left on both sides of the slot-like opening provide tolerance compensation at the clamping forces specified by the customer, taking into consideration also the fact that the material of the lateral band portions is work-hardened by the punching-out operation of the tolerance-compensating opening.
1. A method for providing tolerance compensation in a clamping band made from metal having low elastic stretchability in the longitudinal direction under tensional tightening stresses,comprising the steps of:
(a) preparing a sample of the clamping band with an opening punched-out in a central area, which work-hardens the remaining lateral band portions surrounding the opening,
(b) determining the yield strength and ultimate strength of the work-hardened lateral band portions,
(c) determining the elongation of the sample corresponding to said yield strength and said ultimate strength in terms of percentage elongation, and
(d) calculating the necessary length of the opening in the longitudinal direction as a function of the determined elongation percentages to provide a given tolerance compensation in the clamping band in the presence of tensional forces when theclamping band is in a fully tightened state.
2. A method according to claim 1, further comprising the step of making a clamp structure by utilizing a determined tolerance-compensating opening of width and length providing the tolerance compensation as calculated and capable of withstandingthe maximum clamping forces expected in the clamp structure.
3. A method for imparting elastic stretchability to a full-width clamping band of a clamp structure to compensate for tolerance in the diametric dimension of an object to be fastened thereby, whereby the clamping band is made from a materialhaving relatively low elastic stretchability in the longitudinal direction of the clamping band, and whereby the clamp structure is an open clamp structure having overlapping band portions adapted to be mechanically interconnected to provide apredetermined clamp structure corresponding substantially to the minimum diameter of the object to be fastened thereby when the clamp structure is installed, said method comprising:
determining the yield strength and ultimate strength of the clamping band,
determining the elongation of the clamping band corresponding to said yield strength and said ultimate strength, and
stamping an elongated opening out of the clamping band of such length and width that the remaining portions of the clamping band surrounding the elongated opening can withstand a predetermined tensile load and provide an elongation in theclamping band sufficient to accommodate an expected tolerance range in the outside diametric dimension of the object to be fastened thereby prior to reaching the yield strength of the material from which the clamping band is made,
wherein the length of the elongated opening is calculated as a function of the determined elongation percentages to provide a given tolerance compensation in the presence of tensional forces in the clamping band in a fully tightened state,thereby rendering the clamping band capable of withstanding the maximum clamping force expected in the clamp structure.
4. A method according to claim 3, wherein the stamping step work-hardens the adjacent areas of the clamping band surrounding the opening, and further comprising the step of determining the width and length of the opening on the basis of thecross-section of the work-hardened areas by taking into consideration the yield strength of the work-hardened clamping band material, the maximum tensional stresses expected in the clamping band and the necessary elongation to provide tolerancecompensation prior to reaching said yield strength.
5. A method according to claim 3, wherein the elongated opening is stamped out exclusively within the area of the clamping band and has a width narrower than the normal width of the clamping band.
||FIELD OF THE INVENTION
This invention relates to an open clamp made from a clamping band material having low elastic stretchability in its longitudinal direction which is provided with a tolerance-compensating arrangement to compensate for tolerances in the assembly,consisting, for example, of hose and nipple, on which the hose is to be fastened, and more particularly to a so-called low-profile or earless clamp structure of the type described above.
BACKGROUND OF THE INVENTION
Open clamp structures of the earless type are known in the prior art, for example, as disclosed in my prior U.S. Pat. No. 4,492,004. Though the prior art clamps, as disclosed in this patent, have enjoyed immense commercial success, they maynot be able to accommodate at all times the entire tolerance range of the assembly consisting of nipple and hose as specified by the customer. This is so as the clamping band material such as stainless steel frequently used for such clamp structures hasrelatively low elastic stretchability in the longitudinal direction, which may be inadequate to permit a completely satisfactory clamping action over the entire range of tolerances from the minimum dimension of the hose and of the nipple to the maximumdimension of the hose and of the nipple within their respective tolerance ranges. The problem of tolerance compensation in clamp structures has been recognized already for some time and various solutions have been proposed heretofore. For example, theBritish Patent 778,861 suggested one or more resilient, arcuately shaped compensating portions. Undulations in the clamping band have been proposed in the French Patent 2,470,275 and can also be found in U.S. Pat. Nos. 4,308,648 and 4,919,682. However, to avoid any leakage underneath the undulations, it was necessary to cover the same by the full band width of the inner band portion. Adopting the teachings of the British Patent 1,064,048, the European Patent 0 296 918 suggested to offsetundulations located on opposite sides of a central cut. However, the problem remained with these prior art proposals of assuring an internal clamping surface devoid of any steps, offsets or discontinuities. Moreover, the need to cover the undulationswith the full-width inner band portion of the clamping band resulted in increased cost owing to the increased length of the clamping band required under these circumstances. Additionally, undulations also involve some cost considerations as regards therequisite length of clamping band in the clamp structure. Other proposals to provide some increased elastic stretchability of the clamping band involved cut-outs in the clamping band. For example, zig-zag shaped cut-outs in the band to impart someelasticity were suggested in U.S. Pat. No. 1,705,895. Other configurations in the clamping band for similar purposes can be found in U.S. Pat. No. 4,910,832 and German Patent DE 30 18 383 as also in my own prior U.S. Pat. No. 4,987,651 whichdisclosed concavely shaped lateral band portions enclosing therebetween an at least approximately hourglass-shaped opening. Common to all of these last-mentioned prior art proposals is the fact that they require movement of band portions, not only inthe direction of the tensional forces, i.e., in the longitudinal direction of the clamping band, but also in a direction transverse thereto as they undergo deformation in the presence of tensional forces.
SUMMARY OF THE INVENTION
The present invention is predicated on the discovery that satisfactory tolerance-compensation can be attained by a simple opening cut out of the clamping band which extends in the clamping band longitudinal direction. The opening produced bypunching or stamping out leaves lateral band portions on both sides thereof which represent an area of reduced resistance to elastic stretchability in the longitudinal direction of the clamping band. The total width of the opening or of severalside-by-side openings should be at least as large as the width of any other opening in the clamping band and its length can be readily determined as will be explained more fully hereinafter. A factor to be considered in the tolerance-compensatingarrangement of this invention resides in the fact that punching or stamping out the opening in the clamping band in a conventional manner in effect work-hardens the material in the band portions left in the clamping band. Longitudinally extendingopenings have been proposed heretofore for various reasons such as, for example, to modify the bendability, especially in so-called self-tightening clamps made from spring material seeking to reduce the diametric dimension of the clamp as disclosed inU.S. Pat. No. 4,773,129. Longitudinal openings were also proposed, for example, in my prior U.S. Pat. No. 4,998,326 to compensate for imbalances in the clamp structure. However, the longitudinal cuts or slot-like openings in this last-mentionedpatent had to be located within the area where the overlapping band portions caused the imbalance in order to compensate for the additional weight caused thereby within this area. By contrast, there is no such requirement for the location of thetolerance-compensating opening in accordance with this invention in which the tolerance-compensating opening can be located within a non-overlapping area of the clamping band, i.e., within an area of the non-overlapping clamping band that extends fromthe mechanical connection to the means for tightening the clamp structure. In case the clamp structure also includes some means for avoiding any steps, offsets or discontinuities in the inner clamping surface, the tolerance-compensating arrangement lieswithin an area of non-overlapping clamping band between the means for avoiding any steps, offsets or discontinuities in the inner clamping surface and the mechanical connection. At any rate, the constraints as to location of the tolerance-compensatingopening which exist in some other applications, do not exist for the tolerance-compensating opening of this invention which can be located anywhere at the designer's choice where the tensional forces occur in the clamping band as the latter is tightened. The length and width of the tolerance-compensating opening of this invention is thereby determined by the specified tolerance range which must be satisfied by the clamp structure and the clamping forces to be expected when fully tightened.
BRIEFDESCRIPTION OF THE DRAWINGS
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, oneembodiment in accordance with the present invention, and wherein:
FIG. 1 is a top plan view on a clamp structure of the earless type with a tolerance-compensating arrangement in accordance with the present invention;
FIG. 2 is a side elevational view of the clamp structure of FIG. 1;
FIG. 3 is a transverse cross-sectional view at right angle to the axial direction of the assembled clamp structure in accordance with the present invention;
FIGS. 4a and 4b are partial plan views on a portion of the clamping band provided with a tolerance-compensating opening of this invention and illustrating schematically the effect of the tolerance-compensating opening as a result of the presenceof tensional tightening forces in the clamping band; and
FIG. 5 is a graph illustrating extension in mm. as a function of load in N of a sample of a clamping band having a thickness of 0.8 mm. and a width of 10 mm. with a tolerance-compensating opening of 4.8 mm. in width and 50 mm. in length, inwhich the clamping band material is stainless steel AISI 304.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring now to the drawing wherein like reference numerals are used throughout the various views to designate like parts, the clamp structure generally designated by reference numeral 10 of this invention is a clamp structure similar to thatshown in the prior U.S. Pat. No. 5,191,684 and includes a clamping band 11 having an inner clamping band end portion 11a and an outer clamping band end portion 11b which overlap in the assembled condition of the clamp structure. In order tomechanically close the clamp structure made from flat clamping band material as shown in its flat punched-out position in FIGS. 1 and 2, in the closed circular position shown in FIG. 3, the mechanical connection includes one or more cold-deformeddeep-drawn support hooks 12a and 12b and a guide hook 13 which are adapted to engage, respectively, in the rectangular aperture 14 and in the elongated aperture 15. The support hooks 12a, and 12b as well as the guide hook 13 may thereby be constructedas more fully disclosed in my prior U.S. Pat. No. 4,299,012. In the preassembled, not-yet tightened condition, the support hook 12a nearer the free end of the inner band portion 11a engages in aperture 14 and the guide hook 13 engages in the elongatedaperture 15 while the support hook 12b away from the free end of the inner band portion 11a is located beyond the end of the outer band portion 11b. In the fully installed tightened condition (FIG. 3), the support hook 12b then engages in aperture 14while the adjoining support hook 12a now engages along the edge 15a of the aperture 15, all as disclosed in the prior U.S. Pat. No. 5,191,684. For tightening the clamp structure about the object to be fastened, a tool-engaging means 16 is provided inthe outer band portion 11b and a tool-engaging means 17 is provided in the inner band portion 11a. The tool-engaging means 16 and 17 are thereby in the form of deep-drawn, pressed-out embossments which are partially convexly shaped in cross section asshown in the aforementioned U.S. Pat. No. 5,191,684. The pressed-out tool-engaging means 16 is thereby in the form of a pressed-out longitudinally extending tunnel which has a convex shape of relatively low height with a tool-engaging abutment surface16a and a torque-limiting tool-engaging abutment surface 16b, the latter to prevent over-torquing of the clamp structure as described in the last-mentioned U.S. patent. The tool-engaging embossment 17 in the inner band portion 11a only has onetool-engaging abutment surface 17a and may taper both in height and in width in the circumferential direction toward the free end of the inner band portion 11a. The tool-engaging embossment 17 is thereby integral with the inner band portion 11a exceptwithin the area of the tool-engaging abutment surface 17a pressed-out after a transverse cut in the inner band portion 11a. In transverse cross section, the tool-engaging embossment 17, like embossment 16, is of convex shape having a relatively lowheight which is lower than the height of the tool-engaging embossment 16 so that the tool-engaging embossment 17 can slide underneath the tool-engaging embossment 16. The tool-engaging embossment 16 is thereby pressed out of the clamping band bydeep-drawing cold deformation after two transverse cuts in the clamping band forming the abutment surfaces 16a and 16b. The tool-engaging embossments 16 and 17 may thereby have the shape and dimensions as more fully disclosed in the U.S. Pat. No.5,191,684, the contents of which are incorporated herein by reference. Openings 16 and 19 of semi-circular shape are provided in the clamping band adjacent the tool-engaging abutment surfaces 17a and 16a to permit the tips of the tightening tool of anyconventional appropriate construction (not shown) to extend into these openings so as to increase the effective area of engagement by the tightening tool. These openings 18 and 19 thereby have a maximum width in the clamping band transverse directiongreater than the maximum width of the embossments 16 and 17 so that the flat engaging surfaces of the jaws of the plier-like tool engage not only with the tool-engaging surfaces 16a and 17a but also with parts of the lateral band portions exposed bythese openings, as described also in the aforementioned U.S. Pat. No. 5,191,684.
To assure an internal clamping surface devoid of any steps, offsets or discontinuities, the inner band end portion 11a terminates in a tongue-like extension 21 adapted to engage into a tongue-receiving means which in the illustrated embodiment isformed by a centrally located pressed-out band portion 22 forming a tongue-receiving channel and leaving on both sides thereof lateral band portions 23a and 23b. The lateral band portions 23a and 23b thereby merge into the normal outside diameter of theouter band portion 11a at first step-like portions 24a and 24b radially displacing the lateral band portions 23a and 23b by a radial distance corresponding substantially to the clamping band thickness while the tongue-receiving channel 22 merges into thenormal clamping band at a second step-like portion 25, as also described more fully in my prior U.S. Pat. No. 4,299,012. As the radial displacement produced by the step-like portions 24a and 24b is about equal to the thickness of the clamping band, itis assured thereby that the inner band portion 11a cannot escape outwardly within an area from the step-like portions 24a and 24b to the free end of the outer band portion 11b.
The tolerance-compensating arrangement generally designated by reference numeral 30 consists in accordance with the present invention of a rectangular slot 31 having rounded-off end portions 32a and 32b and leaving lateral band portions 33a and33b on both sides thereof. As can be seen from FIGS. 1 and 3, the opening 30 is located in the band portion within the area intermediate the overlapping band portions 11a and 11b, and more particularly also within the area of the non-overlappingclamping band 11 located between hook-like member 12b of the mechanical connection 12, 13, 14, 15 and the tool-engaging means 16. With an arrangement 22, 23a, 23b, 24a, 24b and 25 to eliminate any step, offset or discontinuity in the internal clampingsurface, the opening 30 is then located between the hook-like member 12b of the mechanical connection and the step-like portion 25 of the tongue-receiving channel 22.
FIGS. 4a and 4b schematically illustrate the operation of the tolerance-compensating arrangement 30 in accordance with the present invention, the distance L representing in FIG. 4a the length of the compensating opening 31 in the non-stressedcondition of the clamping band, laid out flat, while FIG. 4b illustrates the length L' resulting from the application of the tensional tightening forces to the clamping band that cause stretching in the lateral band portions 33a and 33b in the presenceof these tensional forces, the clamping band being again laid out flat in FIG. 4b for purposes of comparison. FIGS. 4a and 4b are thereby not drawn to scale and are only for illustrative purposes.
Typical values for one size clamp which are indicated herein only for purposes of illustration and which can be varied as known to those skilled in the art, are as follows:
The thickness b (FIG. 2) of the clamping band 11 made from stainless steel AISI 304 is 0.8 mm. and the width a (FIG. 1) of the clamping band is 10 mm. The length d of the tongue-like extension 21 is 11 mm., the end of the full width clampingband end portion 11a being chamfered at a 45.degree. angle. The width e of aperture 14 is 4.8 mm. and its length f is 4.7 mm. The length g of the tunnel-shaped embossment 16 is 12.2 mm. and the length h of aperture 15 is 15.9 mm. The distance ifrom the free end of the outer band portion 11b to the transverse end surface 15a of the aperture 15 nearer the free end of the outer band portion is 9.9 mm. and the distance j from the step-like portions 24a and 24b to the end surface 15a of theaperture 15 is 37.1 mm. while the length k of the tongue-receiving channel 22 is 13 mm. The length 1 (FIG. 1) of the slot 31 is 50 mm., the rounded-off end portions 32a and 32b being semi-circular in shape. The distance m from the end of thetongue-like extension 21 to the end of aperture 19 opposite the tool-engaging surface 17a is 35 mm., the distance from the end of the tongue-like extension 21 to the end of the first support hook 12a nearer the free end of the tongue-like extension 21 is45.6 mm., the distance o from the end of the tongue-like extension to the end of the second support hook 12b is 52.5 mm. and the distance p from the end of the tongue-like extension 21 to the end of the full-width rectangular portion of opening 31nearer the free end of the inner band portion 11a is 62 mm. The width q of the tongue-receiving channel 22 is 4.2 mm., the width r of the tongue-like extension 21 is 4 mm. and the distance s from the end of the tongue-like extension 21 to the end ofthe guide hook 13 is 41.2 mm. The maximum width of the tool-engaging embossment 17 is about 3.8 mm. The width w of opening 31 is 4.8 mm. while the lateral band portions 33a, 33b each have a width in the transverse direction of 2.6 mm. As the width wof opening 31 is increased, the width of the lateral band portions 33a and 33b will decrease, thereby reducing resistance of the latter to elastic stretching in the longitudinal direction of the clamping band in the presence of tensional forces. Theoverall length a (FIG. 2) can be chosen at will for a given nominal diametric dimension of the clamp structure, only the dimensions indicated hereinabove being important for any given diameter size. The openings 18 and 19 are made with a radius of 4.5mm. and may each include a small portion beyond the semi-circle which extends rectilinearly in the direction of the clamping band longitudinal direction. The foregoing dimensional indications are only for purposes of illustration and may be varied asknown to those skilled in the art to suit any particular clamp design. For example, it is also possible, depending on width of the clamping band to substitute for the single central opening 30 two or more slot-like openings in the clamping band whichextend in the longitudinal direction of the clamping band as long as the total area of these openings corresponds to the needed area to provide the required tolerance compensation in the remaining clamping band portions.
The length and width of the tolerance-compensating opening 30 can be readily determined empirically. It is only necessary to make a test sample of the band material from which the clamping band is made, cut an opening of a certain width andlength, and then subject the test sample in steps to ever-increasing tensional forces until the tensional forces are reached which are expected in the fully tightened clamp structure. By measuring the increase in length (stretching) and noting thesubsequent elastic return of the test sample, one can arrive in a short time by trial and error at the proper length and width for the opening 30 with a given material, whereby prior experience with a given material will permit short-cuts in thisapproach, which must also take into consideration the necessity that the clamp structure with such opening must be able to pass satisfactorily all leakage tests normally required of a given clamp structure. This can be assured, if needed, by a trade-offin the width of the opening versus its length.
A more scientific approach is as follows. Taking a stainless steel clamping band material having a yield strength of 345 MPa, a slot-like opening 4.8 mm. wide and 54.8 mm. long with 2.4 mm. radius at each end is punched out of the centralarea of the clamping band having a width of 10 mm. and a thickness of 0.8 mm., thereby leaving lateral band portions of 2.6 mm. on each side of the slot-like opening. This means that the clamping band has a remaining cross-sectional area of
2 (W.times.T)=2 (2.6.times.0.8)=4.16 mm.sup.2
The raw material having a rated yield strength of 345 MPa would assure that the clamping band in the slot area would withstand a tensile load of 1434 N (345.times.4.16) prior to exceeding the yield point. However, stamping the slot-like openingout of the clamping band, work-hardens the material so that the yield point increases. The elongation at yield point as determined by tests, then becomes 1.4 mm. which translates to an increase of about 0.5 mm. in clamp diameter without exceeding theclamping band material yield strength.
Taking a clamp structure described in the typical example made from 304 AISI stainless steel with a band width of 10 mm. and a thickness of 0.8 mm.
the yield strength of the raw material=392 N/mm.sup.2, and
its ultimate strength=654 N/mm.sup.2.
The mechanical properties increase as the material is cold-worked, i.e., stamping the slot will increase the yield strength and ultimate strength as follows:
Yield strength with slot configuration=549 N/mm.sup.2 and
Ultimate strength with slot configuration=705 N/mm.sup.2.
The yield strength with slot configuration leaving band portions of 2.6 mm. on each side of the 4.8 mm. slot-like opening will therefore be
2 (W.times.T).times.579=2408 N
This translates into an elongation of 1.7 mm., as can be seen from the graph of FIG. 5, representing a typical load v. extension graph for the sample with slot configuration. The 1.7 mm. elongation corresponds to a diameter increase, notexceeding yield strength=1.7/.pi., thus providing a diameter increase .DELTA. diameter of about 0.54 mm.
The ultimate yield strength with slot configuration would be 2 (W.times.T).times.705=2934 N.
As can be seen from the graph of FIG. 5, at ultimate strength of 2934 N, the elongation would be 10.74 mm. which corresponds to a diameter compensation, not exceeding ultimate strength, of 0.27 mm.
The elongation can be referred to as a percentage of the original graph length (L) which percentage remains constant.
In the example an elongation of 0.54 mm. represents an elongation of 3.4%. For example, with a length L=25 mm., the diameter compensation would be
While I have shown and described only one embodiment in accordance with the present invention, it is understood that the tolerance-compensating arrangement of this invention is not limited thereto but may be applied to any other type of clampstructure in which certain tolerance compensation must be achieved to meet a customer's requirements. For example, the tolerance-compensating arrangement of this invention may also be used with a clamp having a typical so-called "Oetiker" ear as shownand described in my prior U.S. Pat. No. 4,299,012 or in my U.S. Pat. No. 5,339,496 to issue on Aug. 23, 1994. It may also be used with a clamp, for example, as shown and described in U.S. Pat. No. 5,564,167 and entitled "Clamp Structure WithSawtooth-Like Locking Arrangement", the subject matter of which is incorporated herein by reference. Additionally, though the mechanical connection consisting of hooks 12 and 13 and apertures 14 and 15 are of the type shown and described in my priorU.S. Pat. No. 4,299,012, the guide hook 12 may also be replaced by a combined guide and support hook as shown and disclosed in my prior U.S. Pat. No. 4,622,720. Furthermore, any other known mechanical connection for the overlapping band end portionsmay be used. As mentioned above, the tightening arrangement may also be replaced by a so-called "Oetiker" ear provided with reinforcing means, for example, as disclosed in my prior U.S. Pat. No. 3,475,793 or preferably in the shape of a shallowdepression of substantially rectangular configuration as disclosed in my prior U.S. Pat. No. 5,282,295. In lieu of a single depression, also two substantially parallel reinforcing depressions may be used in the bridging portion which encompasses thesame total area mentioned in U.S. Pat. No. 5,282,295 or in my copending application Ser. No. 07/629,716, filed Dec. 18, 1990 and entitled "Reinforced Ear Structure for Clamps," the subject matter of which is incorporated herein. Moreover, the means21, 22, 23, 24 and 25 of this invention to assure an internal clamping surface devoid of any step, offset or discontinuity, may also be achieved as disclosed in my prior U.S. Pat. No. 4,315,348 or in my prior U.S. Pat. No. 4,237,584 or as disclosedin FIGS. 6 to 11 of my prior U.S. Pat. No. 5,283,931. Thus, the present invention is not limited to the particular embodiments as shown and described herein and/or to their dimensions as described herein but is applicable to other modified clampstructures involving similar problems. I therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.
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